a. Field of the Invention
The present invention relates generally to orthotic devices for feet, and more particularly, to a thin, substantially rigid orthotic formed of molded material and having a shape for controlling and directing the motions of a foot.
b. Related Art
Orthotic inserts (referred to herein as “orthotics”) are devices intended to be placed in shoes and other footwear to cooperate with the plantar surfaces of the wearer's feet.
Orthotic inserts can be either soft or hard. Soft inserts are typically constructed of one or more layers of resiliently compressible foam material, with the foam being thicker in some areas and thinner in others to provide particular contour with respect to a foot. The cushioning effect of the foam material, which compresses under the weight of the foot, is often seen as the primary benefit of such devices, but this is in fact somewhat misleading. Although a degree of cushioning is indeed desirable for certain applications, such as for use in running, hiking and athletic shoes, the most significant benefit of an orthotic insert comes from its ability to control and direct the motions of the foot as the foot progresses through the gait cycle. As is known, the foot progresses from a “mobile adapter” phase at heel strike, in which the foot flexes and absorbs impact loads, to a “rigid lever” at toe-off phase in which the foot locks up for effective propulsion. This biomechanical action is dependent on the proper locking and unlocking of the joint structure of the foot, which in turn is dependent on the proper motion of the foot. It is therefore a primary concern that the orthotic device provide proper control and direction of these motions.
Due to their yielding and flexible nature, it is difficult for soft, foam orthotics to exert the requisite degree of control over the motions of the foot. These difficulties have been overcome in certain soft orthotics through the addition of various stiffening or supporting elements formed of a comparatively rigid or less compressible material. For example, some soft orthotics employ an underlying rigid cap that is configured to provide the foam layers with added support and resistance in selected areas. Nevertheless, the control over the motions of the foot is inevitably compromised to one degree or another by the soft, yielding nature of the foam material.
As noted above, the cushioning qualities of compressible material provides make the trade-off worthwhile in the case of certain high-impact activities. For dress shoes, however, the cushioning qualities of the soft orthotic are of comparatively little benefit, even though control of the motions of the foot remains essential. Moreover, dress shoes, as compared with running, hiking or athletic shoes, are traditionally constructed with relatively tight-fitting uppers, so that there is very little excess room in the shoe to accommodate the height that is inherent in a soft, compressible orthotic device, especially since (as noted above) the best of the soft devices have a built-up construction using layers of foam and more rigid materials. As a result, using a soft orthotic in a dress shoe frequently causes the foot to be squeezed against the upper, causing discomfort and possibly creating abrasion and blisters. This is especially true in the case of the typical consumer, where the shoe is fitted only to the foot at the time of purchase and the consumer wishes to install an orthotic insert at a later time.
Rigid orthotic inserts tend to be thinner than soft orthotic inserts, and are therefore frequently more suited to use in a dress shoe. Moreover, rigid orthotic inserts, as a class, offer the prospect of increased control over the motions of the foot. However, prior rigid orthotics inserts have exhibited drawbacks of their own. Many of these devices have been constructed using cast urethane, which is comparatively thick and heavy and also tends to crack with extended use. In this regard, it should be understood that while “rigid” orthotics have a high degree of rigidity as compared with soft orthotics, a certain degree of flexibility and a high level of resilience are still required in order to accommodate the flexing and bending motions of the foot and insole.
Other rigid inserts have been constructed using layers of fiberglass-resin and graphite fiber-resin material, which gives a near optimal combination of thinness, strength and durability, but at a comparatively high cost: not only are the fiber-resin materials comparatively expensive, but manufacture of the inserts requires a fairly involved and labor-intensive process in which the layers are cut from sheets of material and then laminated and shaped over a cast or other form. As a result, fiber-resin construction is usually reserved for high-end, custom or semi-custom orthotics. However, not only are the costs of custom orthotics generally beyond the budgets of many consumers, but in fact the bulk of the benefits can be achieved using a standardized orthotic, provided that it has the right shape and other qualities for controlling and directing motions of the foot.
Accordingly, there exits a need for an orthotic insert having sufficient rigidity to properly control the motions of the foot that can be manufactured efficiently and at low cost. Furthermore, there exists a need for such an orthotic insert that has sufficient resilient flexibility that it is able to bend together with the foot and shoe as the foot progresses through the gait cycle. Still further, there exists a need for such an orthotic insert that maintains the correct shape and contour such that the foot is properly supported and controlled in the shoe. Still further, there exists a need for such an orthotic insert that has a thin vertical dimension so that the orthotic insert can be used in a conventional dress shoe without crowding the foot therein. Still further, there exists a need for such an orthotic insert that is durable and long lasting in service and is resistant to cracking and other sources of failure.